Fifteen years after the 9/11 terrorist attacks, a Senate committee probed senior counterterrorism officials about their efforts.

Fifteen years after the 9/11 terrorist attacks, counterterrorism efforts expand beyond the physical world to social media and encrypted communications, where federal workers actively try to prevent terrorists from radicalizing potential attackers online.

That's how three top senior counterterrorism officials described their sprawling challenge to a Senate committee Tuesday, where they faced questions about how they could better use technology to prevent future attacks. The hearing was held shortly after the anniversary of 9/11, and also within months and days of the Pulse nightclub shooting in Orlando as well as a series of pipe- and pressure-cooker bombs detonating in the New York City area.

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FBI Director James Comey said the bureau uses sources and undercover agents to identify people who are at risk of radicalizing or who are transitioning from simply consuming information to actively planning attacks. "We are making good progress with the help of companies like Twitter at chasing the Islamic State" off the platform—the microblogging site has suspended hundreds of thousands of accounts promoting terrorism—but Comey said the challenge is that such efforts push some users "to a place where they’re less able to proselytize broadly but more able to communicate in a secure way. [We've] chased them to apps like Telegram.”

The bureau's mission is to understand what kind of activity takes place in those encrypted spaces, he said.

But the “increasing ability of terrorist actors to communicate with each other outside our reach" makes tracking terrorist plots more difficult, said Nicholas Rasmussen, director of the National Counterterrorism Center within the Office of the Director of National Intelligence, during the hearing.

Here are a few other takeaways:

1. Congress wants to know exactly how the Department of Homeland Security will counter violent extremism.

DHS' new Office of Community Partnerships, established one year ago with the mission of fighting violent extremism by preventing ISIS from forming relationships with potential attackers, has not yet put forth a detailed plan about their operations, Secretary Jeh Johnson testified during the hearing.

Johnson said the plan should be available sometime during the month of October. He said the strategy would likely be to develop a counter-narrative "within the community" to ISIS messaging, but that a purely government-written message would appear inauthentic.

2. The FBI needs Congress' help in getting electronic records.

For many years, law enforcement could issue national security letters for phone transaction records as well as internet records, Comey explained. "Several years ago, lawyers for some reason started to interpret the statute [as though] it wouldn't allow them to get internet records in a way that they could for telephony," he said.

He asked for Congress' help in specifying that the letters could apply to both internet and phone records, which Sen. Kelly Ayotte, R-N.H., pointed out is common practice in criminal cases.

3. Watchlists could be getting higher tech.

The past two administrations have created an "end-to-end watchlist system" that gives counterterrorism teams "confidence that if we have an identity, we are very likely to be able to prevent an individual from getting into the United States," Rasmussen said. But the country's ability to track those people depends on partner groups sharing data with counterterrorism teams, he said.

And the watchlist system could soon evolve, he added. "It is still a name-based system, and over time it needs to transition to a biometrics-based system," he said, especially because criminals attempt to evade apprehension by creating false documents.

4. DHS' fingerprints records could be digitized in the next year.

A recent audit by DHS' inspector general found that the department may have erroneously granted citizenship to hundreds of people who were flagged for deportation because of incomplete fingerprint records; adjudicators must check a candidate's fingerprints before granting citizenship to make sure they haven't been deported under a different name, but in some cases those were absent because they hadn't been digitized yet.

Asked whether any of them could have been terrorists or suspects, Johnson said he had "no basis to believe" that was the case, but added that the process for digitizing prints should be completed in the next nine months.

5. DHS is helping 18 states protect their voter databases.

The department helps state and local officials "with their cybersecurity when they ask," Johnson said, referring to a rash of reports of intrusions, possibly foreign, into state voter databases. So far, 18 states have asked for help, he said.

There are a "limited number" of cases of intrusions to "get into the online presence of various state election agencies," Johnson said, adding "one or two of them have been successful."